Self-interference-cancelled full-duplex relays

ABSTRACT

A relay including a first transmitter that converts a first digital transmit signal to a first analog transmit signal, a first receiver that converts a first analog receive signal to a first digital receive signal, a second transmitter that converts a second digital transmit signal to a second analog transmit signal, a second receiver that converts a second analog receive signal to a second digital receive signal, and a self-interference canceller that generates a first self-interference cancellation signal based on at least one of the first digital transmit signal and the first analog transmit signal, and combines the first self-interference cancellation signal with at least one of the first digital receive signal and the first analog receive signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/473,653, filed on 29 Aug. 2014, which claims the benefit of U.S.Provisional Application Ser. No. 61/871,519, filed on 29 Aug. 2013, bothof which are incorporated in their entirety by this reference.

TECHNICAL FIELD

This invention relates generally to the wireless communications field,and more specifically to new and useful full-duplex relays.

BACKGROUND

In many wireless communication networks, there are areas that are noteasily covered by access points due to signal attenuation by terrain orother structural obstacles. One approach to extending access pointsignal coverage involves using relay nodes that rebroadcast signalsoriginating from and/or destined to access points.

One major roadblock to successful implementation of relays is theproblem of self-interference; relays may suffer from issues resultingfrom cross-talk between transmitters and receivers, duplexer leakages,or other undesired electromagnetic couplings. Many modern relays usefrequency or time division multiplexing techniques or antenna separationtechniques to address self-interference. Each of these techniques hassubstantial drawbacks: frequency division multiplexing requires doublingspectrum usage, time division multiplexing requires halving signalcapacity, and antenna separation is often expensive, if not impossiblegiven space constraints. Full-duplex relays may addressself-interference without any of these drawbacks. Thus, there is a needin the wireless communications field to create new and usefulfull-duplex relays. This invention provides such new and usefulfull-duplex relays.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram representation of a system of a preferredembodiment;

FIGS. 2A, 2B, and 2C are diagram representations of antenna couplings ofa system of a preferred embodiment;

FIG. 3 is a schematic representation of a receiver of a system of apreferred embodiment;

FIG. 4 is a schematic representation of a transmitter of a system of apreferred embodiment;

FIG. 5 is a diagram representation of a self-interference canceller of asystem of a preferred embodiment;

FIG. 6 is a diagram representation of a self-interference canceller of asystem of a preferred embodiment;

FIGS. 7A and 7B are diagram representations of a digitalself-interference canceller of a system of a preferred embodiment;

FIG. 8 is a diagram representation of a system of a preferredembodiment;

FIG. 9 is a diagram representation of a system of a preferredembodiment;

FIGS. 10A, 10B and 10C are diagram representations of antenna couplingsof a system of a preferred embodiment; and

FIG. 11 is a diagram representation of a system of a preferredembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiments of the inventionis not intended to limit the invention to these preferred embodiments,but rather to enable any person skilled in the art to make and use thisinvention.

As shown in FIG. 1, a relay 100 includes a first receiver 110, a firsttransmitter 120, a second receiver 115, a second transmitter 125, and aself-interference canceller 130. The relay 100 functions to repeatcommunication signals (and/or information contained in communicationsignals, herein referred to as “messages”) transmitted and receivedbetween two communications systems. In addition to repeating signals,the relay 100 preferably cancels self-interference between transmittedand received signals. The relay 100 may additionally or alternativelyscale (e.g. amplify, attenuate), shift, or otherwise modify signalsreceived or transmitted by the relay 100.

The relay 100 is preferably used to repeat communication signalstraveling bi-directionally between two wireless communication systems(e.g. a cell-phone tower and a cell phone, or a Wi-Fi™ access point anda computer, two wireless radios), but may additionally or alternativelybe used to repeat communications signals between any other suitablewired or wireless communication systems. In a variation of a preferredembodiment, the relay 100 is a one-way relay and includes only a firstreceiver 110, a first transmitter 120, and a self-interference canceller130.

The relay 100 is preferably implemented using both digital and analogcircuitry. Digital circuitry is preferably implemented using ageneral-purpose processor, a digital signal processor, an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA) and/or any suitable processor(s) or circuit(s). Analog circuitryis preferably implemented using analog integrated circuits (ICs) but mayadditionally or alternatively be implemented using discrete components(e.g., capacitors, resistors, transistors), wires, transmission lines,waveguides, digital components, mixed-signal components, or any othersuitable components. The relay 100 preferably includes memory to storeconfiguration data, but may additionally or alternatively be configuredusing externally stored configuration data or in any suitable manner.

In one example implementation, the relay 100 is used as a cellularrepeater. The relay 100 is connected to a cell tower by a firstcommunications link using a first transmit/receive antenna coupled tothe relay 100 by a duplexer, and to a cell phone by a secondcommunications link using a second transmit/receive antenna coupled tothe relay 100 by a duplexer. The cell phone and cell tower nativelycommunicate in an uplink frequency (from phone to tower) and a downlinkfrequency (from tower to phone). The relay 100 receives and re-transmitscommunication on both the uplink frequency (phone to relay to tower) andthe downlink frequency (tower to relay to phone). The self-interferencecanceller 130 enables full-duplex operation for the firsttransmit/receive antenna and the second transmit receive/antenna. Thisis distinct from traditional relays, which must rely on techniques liketime-division multiplexing or antenna isolation to avoidself-interference. More specifically, the self-interference canceller130 may enable the relay 100 to receive downlink communications (fromtower to relay), retransmit downlink communications (from relay tophone), receive uplink communications (from phone to relay), andretransmit uplink communications (from relay to tower) simultaneously,without requiring antennas to be isolated from one another, the use ofadditional frequencies, or the use of time multiplexing (because theself-interference canceller 130 reduces self-interference that mayotherwise prohibit such operation). Thus, the relay 100 is able toprovide network-relaying capability without excess cost, excess spectrumusage, or significantly decreased data capacity.

The first receiver 110 functions to receive analog receive signalstransmitted by a first communications system over a first communicationslink (e.g., a wireless channel, a coaxial cable). The first receiver 110preferably converts analog receive signals into digital receive signalsfor processing before re-transmission by the first transmitter 120, butmay additionally or alternatively not convert analog receive signals(passing them through directly without conversion).

The first receiver 110 is preferably a radio-frequency (RF) receiver,but may additionally or alternatively be any suitable receiver.

The first receiver 110 is preferably coupled to the first communicationslink by a duplexer-coupled RF antenna as shown in FIG. 2A, but mayadditionally or alternatively be coupled to the first communicationslink in any suitable manner. Some examples of alternative couplingsinclude coupling via one or more dedicated receive antennas (as shown inFIG. 2B). In another alternative coupling, the first receiver 110 may becoupled to the first communications link by a circulator-coupled RFantenna as shown in FIG. 2C.

The first receiver 110 preferably includes an analog-to-digitalconverter (ADC) in and a frequency downconverter 112, as shown in FIG.3. The first receiver no may additionally or alternatively includeamplifiers, filters, signal processors and/or any other suitablecomponents. In one variation of a preferred embodiment, the firstreceiver 110 includes only analog processing circuitry (e.g.,amplifiers, filters, attenuators, delayers). The first receiver mayfunction to scale, shift, and/or otherwise modify the receive signal.The downconverter 112 functions to downconvert the analog receive signalfrom RF (or any other suitable frequency) to a baseband analog receivesignal, and the analog-to-digital converter (ADC) in functions toconvert the baseband analog receive signal to a digital receive signal.

The ADC 111 may be any suitable analog-to-digital converter; e.g., adirect-conversion ADC, a flash ADC, a successive-approximation ADC, aramp-compare ADC, a Wilkinson ADC, an integrating ADC, a delta-encodedADC, a time-interleaved ADC, or any other suitable type of ADC.

The frequency downconverter 112 functions to downconvert the carrierfrequency of the analog receive signal to baseband, preparing it forconversion to a digital receive signal. The downconverter 112 preferablyaccomplishes signal downconversion using heterodyning methods, but mayadditionally or alternatively use any suitable upconversion methods.

The downconverter 112 preferably includes a local oscillator (LO), amixer, and a baseband filter. The local oscillator functions to providea frequency shift signal to the mixer; the mixer combines the frequencyshift signal and the analog receive signal to create (usually two)frequency shifted signals, one of which is the baseband signal, and thebaseband filter rejects signals other than the baseband analog receivesignal.

The local oscillator is preferably a digital crystal variable-frequencyoscillator (VFO) but may additionally or alternatively be an analog VFOor any other suitable type of oscillator. The local oscillatorpreferably has a tunable oscillation frequency but may additionally oralternatively have a static oscillation frequency.

The mixer is preferably an active mixer, but may additionally oralternatively be a passive mixer. The mixer may comprise discretecomponents, analog ICs, digital ICs, and/or any other suitablecomponents. The mixer preferably functions to combine two or moreelectrical input signals into one or more composite outputs, where eachoutput includes some characteristics of at least two input signals.

The baseband filter is preferably a lowpass filter with a tunablelow-pass frequency. Additionally or alternatively, the baseband filtermay be a lowpass filter with a set low-pass frequency, or any othersuitable type of filter. The baseband filter is preferably a passivefilter, but may additionally or alternatively be an active filter. Thebaseband filter is preferably implemented with analog circuitcomponents, but may additionally or alternatively be digitallyimplemented.

The second receiver 115 functions to receive analog receive signalstransmitted by a second communications system over a secondcommunications link (e.g., a wireless channel, a coaxial cable). Thesecond receiver 115 preferably converts analog receive signals intodigital receive signals for processing before re-transmission by thesecond transmitter 125, but may additionally or alternatively notconvert analog receive signals (passing them through directly withoutconversion).

The second receiver 115 preferably includes an analog-to-digitalconverter (ADC) 116 and a frequency downconverter 117, as shown in FIG.3. The second receiver 115 is preferably substantially similar to thefirst receiver 110, but may additionally or alternatively be anysuitable receiver.

The first transmitter 120 functions to retransmit signals received bythe first receiver 110. The first transmitter 120 preferably convertsdigital transmit signals into analog transmit signals, but mayadditionally or alternatively receive and retransmit analog transmitsignals from the first receiver 110, thus avoiding digital-to-analogconversion. The transmit signals are preferably formed by processingreceive signals (which may include analog-to-digital conversion orfrequency shifting, for example) by the first receiver 110, but thetransmit signals may additionally or alternatively be any signalintended for transmission by the relay 100. The first transmitter 120preferably transmits signals over a second communications link to asecond communications system; these signals are preferably retransmittedsignals from a first communication system sent to the relay 100 over afirst communications link, but may additionally or alternatively be anysuitable signals.

The first transmitter 120 is preferably a radio-frequency (RF)transmitter, but may additionally or alternatively be any suitabletransmitter.

The first transmitter 120 is preferably coupled to the secondcommunications link by a duplexer-coupled RF antenna as shown in FIG.2A, but may additionally or alternatively be coupled to the secondcommunications link in any suitable manner. Some examples of alternativecouplings include coupling via one or more dedicated transmit antennas(as shown in FIG. 2B). In another alternative coupling, the firsttransmitter 120 may be coupled to the second communications link by aduplexer-coupled RF antenna as shown in FIG. 2C.

The first transmitter 120 preferably includes a digital-to-analogconverter (DAC) 121 and a frequency upconverter 122, as shown in FIG. 4.The first transmitter 120 may additionally or alternatively includeamplifiers, filters, signal processors and/or any other suitablecomponents. The first transmitter 120 may function to scale, shift,and/or otherwise modify the transmit signal. The digital-to-analogconverter (DAC) 121 functions to convert the digital transmit signal toa baseband analog transmit signal, and the upconverter 122 functions toupconvert the baseband analog transmit signal from baseband to RF (orany other intended transmission frequency).

The DAC 121 may be any suitable digital-to-analog converter; e.g., apulse-width modulator, an oversampling DAC, a binary-weighted DAC, anR-2R ladder DAC, a cyclic DAC, a thermometer-coded DAC, or a hybrid DAC.

The frequency upconverter 122 functions to upconvert the carrierfrequency of the baseband analog transmit signal to a radio frequency,preparing it for transmission over the communications link. Theupconverter 122 preferably accomplishes signal upconversion usingheterodyning methods, but may additionally or alternatively use anysuitable upconversion methods.

The upconverter 122 preferably includes a local oscillator (LO), amixer, and an RF filter. The local oscillator functions to provide afrequency shift signal to the mixer; the mixer combines the frequencyshift signal and the baseband analog transmit signal to create (usuallytwo) frequency shifted signals, one of which is the RF analog transmitsignal, and the RF filter rejects signals other than the RF analogtransmit signal.

The local oscillator is preferably a digital crystal variable-frequencyoscillator (VFO) but may additionally or alternatively be an analog VFOor any other suitable type of oscillator. The local oscillatorpreferably has a tunable oscillation frequency but may additionally oralternatively have a static oscillation frequency.

The mixer is preferably an active mixer, but may additionally oralternatively be a passive mixer. The mixer may comprise discretecomponents, analog ICs, digital ICs, and/or any other suitablecomponents. The mixer preferably functions to combine two or moreelectrical input signals into one or more composite outputs, where eachoutput includes some characteristics of at least two input signals.

The RF filter is preferably a bandpass filter centered around a tunableradio frequency. Additionally or alternatively, the RF filter may be abandpass filter centered around a set radio frequency, or any othersuitable type of filter. The RF filter is preferably a passive filter,but may additionally or alternatively be an active filter. The RF filteris preferably implemented with analog circuit components, but mayadditionally or alternatively be digitally implemented.

The second transmitter 125 functions to retransmit signals received bythe second receiver 115. The second transmitter 125 preferably convertsdigital transmit signals into analog transmit signals, but mayadditionally or alternatively receive and retransmit analog signals fromthe second receiver 115, thus avoiding digital-to-analog conversion. Thetransmit signals are preferably formed by processing receive signals(which may include analog-to-digital conversion or frequency shifting,for example) by the second receiver 115, but the transmit signals mayadditionally or alternatively be any signal intended for transmission bythe relay 100. The second transmitter 125 preferably transmits signalsover a first communications link to a first communications system; thesesignals are preferably retransmitted signals from a second communicationsystem sent to the relay 100 over a second communications link, but mayadditionally or alternatively be any suitable signals.

The second transmitter 125 preferably includes a digital-to-analogconverter (DAC) 126 and a frequency upconverter 127, as shown in FIG. 4.The second transmitter 125 is preferably substantially similar to thefirst transmitter 120, but may additionally or alternatively be anysuitable transmitter.

The self-interference canceller 130 functions to reduceself-interference in the relay 100 by canceling self-interferencecomponents present in receive signals of the relay 100. Theself-interference canceller 130 preferably includes one or more analogself-interference cancellers 131; the self-interference canceller 130may additionally or alternatively include a digital self-interferencecanceller 132, as shown in FIG. 5.

Analog self-interference cancellers 131 preferably reduceself-interference by sampling an analog transmit signal and generatingan analog self-interference cancellation signal based on the inputanalog transmit signal. The analog self-interference cancellation signalis preferably combined with an analog receive signal before the analogreceive signal is received by a receiver (e.g., 110 or 115), but mayadditionally or alternatively be combined with the receive signal at anysuitable location or time.

Analog self-interference cancellers 131 preferably generateself-interference cancellation signals for a given analog receive signalfrom a corresponding direction analog transmit signal as shown in FIG. 5(e.g., the self-interference cancellation signal combined with are-transmitted uplink signal is preferably generated from the receiveduplink signal). Additionally or alternatively, analog self-interferencecancellers 131 may generate self-interference cancellation signals for agiven analog receive signal from any other analog transmit signal.

For example, in situations where the relay 100 relays bi-directionalcommunication (e.g., uplink/downlink) on well-separated frequencies,self-interference in the downlink receiver occurring from the uplinktransmitter may be negligible (or vice versa); however, in situationswhere the uplink and downlink frequencies are closer, self-interferencemay occur across channels (e.g., when uplink/downlink channels are inthe same frequency band). In these situations it might be desirable tohave hetero-channel as well as homo-channel self-interferencecancellation, as shown in FIG. 6.

The analog self-interference canceller 131 is preferably implemented asan analog circuit that transforms an analog transmit signal into ananalog self-interference cancellation signal by combining a set offiltered, scaled, and/or delayed versions of the analog transmit signal,but may additionally or alternatively be implemented as any suitablecircuit. For instance, the analog self-interference canceller 131 mayperform a transformation involving only a single version or copy of theanalog transmit signal. The transformed signal (i.e. the analogself-interference cancellation signal) preferably represents at least apart of the self-interference component received at a coupling point ofthe relay 100 to a communications link (e.g. a receive antenna).

The analog self-interference canceller 131 is preferably adaptable tochanging self-interference parameters in addition to changes in theanalog transmit signal; for example, transmitter temperature, ambienttemperature, antenna configuration, humidity, and transmitter power.Adaptation of the analog self-interference canceller 131 is preferablyperformed by a control circuit or other control mechanism included inthe canceller 131, but may additionally or alternatively be performed byany suitable controller.

The analog self-interference canceller 131 is preferably coupled tosignal paths by short section directional transmission line couplers,but may additionally or alternatively be coupled by any power dividers,power combiners, directional couplers, or other types of signalsplitters suitable for coupling signal paths of the relay 100 to theanalog self-interference canceller 131.

The digital self-interference canceller 132 functions to reduceself-interference in the relay 100 by canceling self-interferencecomponents present in digital receive signals. The digitalself-interference canceller 132 preferably performs both linear andnon-linear digital self-interference cancellation, but alternatively mayonly perform one of the two.

The digital self-interference canceller 132 preferably reduces digitalself-interference by sampling one or more digital transmit signals andgenerating one or more digital self-interference cancellation signalsbased on input sampled digital transmit signals (and a transformconfiguration). Digital self-interference cancellation signals may becombined with corresponding receive signals at any time or location. Thedigital self-interference canceller 132 preferably removesself-interference signal components not removed by analogself-interference cancellers 131.

The digital self-interference canceller 132 preferably samples digitaltransmit signals of the relay 100 (additionally or alternatively, thecanceller 132 may sample analog transmit signals or any other suitabletransmit signals) and transforms the digital transmit signals to digitalself-interference cancellation signals based on one or more digitaltransform configurations. The digital transform configuration preferablyincludes settings that dictate how the digital self-interferencecanceller 132 transforms a digital transmit signal to a digitalself-interference cancellation signal (e.g. coefficients of ageneralized memory polynomial used to transform the transmit signal to aself-interference signal).

The digital self-interference canceller 132 preferably generatesself-interference cancellation signals for a given digital receivesignal from a corresponding direction digital transmit signal as shownin FIG. 7A (e.g., the self-interference cancellation signal combinedwith a re-transmitted uplink signal is preferably generated from thereceived uplink signal). Additionally or alternatively, the digitalself-interference canceller 132 may generate self-interferencecancellation signals for a given digital receive signal from any othertransmit signal or combination of transmit signals (including analogtransmit signals converted using ADCs).

For example, in situations where the relay 100 relays bi-directionalcommunication (e.g., uplink/downlink) on well-separated frequencies,self-interference in the downlink receiver occurring from the uplinktransmitter may be negligible (or vice versa); however, in situationswhere the uplink and downlink frequencies are closer, self-interferencemay occur across channels. In these situations it might be desirable tohave hetero-channel as well as homo-channel self-interferencecancellation, as shown in FIG. 7B.

Each self-interference cancellation signal generated by the digitalself-interference canceller 132 is preferably associated with aconfiguration transform (e.g., t1, t2, t3, and t4 of FIGS. 7A and 7B);additionally or alternatively, configuration transforms may beassociated with digital self-interference cancellation signals in anysuitable manner.

In the above description of the preferred embodiments, it is mentionedthat the relay 100 may form transmit signals by processing receivesignals (e.g., by phase shifting, amplifying, attenuating, frequencyshifting, etc.). In a variation of a preferred embodiment, processingmay be performed by relay bases 140 positioned between transmitters andreceivers, as shown in FIG. 8. A relay base 140 may be a layer 1 (L1)relay, a layer 2 (L2) relay, a layer 3 (L3) relay, or any other suitablerelay. Relay bases 140 preferably function to prepare signals forretransmission; for example, a relay base 140 may reorganize informationbefore retransmitting to increase transmission efficiency. As anotherexample, a relay base 140 may delay a signal before retransmission totime it with a particular transmission window.

While the examples above are directed to single-in/single-out (SISO)relays, it is understood that the relay 10 o may also be used formultiple-in/multiple-out (MIMO) communications, as shown in FIG. 9. MIMOtechnology may offer increased data throughput and link range withoutthe need for additional bandwidth or increased transmitter power.

The example relay 100 as shown in FIG. 9 represents a 2×2 MIMO system,but it is understood that the relay 100 may additionally oralternatively utilize any suitable number of transmit and receivesignals. Each signal path may have separate antennas; alternatively,signal paths may share antennas via a duplexer or other coupler. In oneexample, each signal path of a 2×2 MIMO relay has four antennas: a TX1antenna, a TX2 antenna, an RX1 antenna, and an RX2 antenna, as shown inFIG. 10A. In another example, each signal path of a 2×2 MIMO system hastwo antennas: a TX1/RX1 antenna (coupled to both TX1 and RX1 signalpaths via a circulator) and a TX2/RX2 antenna (coupled to both TX2 andRX2 signal paths via a circulator), as shown in FIG. 10B. In a thirdexample, each signal path of a 2×2 MIMO system is again associated withfour antennas, but the relay 100 has only four antennas total; aduplexer is used to couple each antenna to both a TX and an RX signal(where the TX and RX signals are from different signal paths), as shownin FIG. 10C.

As shown in FIGS. 10A and 10B, the first and second transmitters 120 and125 are preferably implementations having multiple inputs and outputs.In particular, each transmitter preferably includes a DAC and frequencyupconverter for each transmit signal path; additionally oralternatively, transmit signal paths may share DACs and/or frequencyupconverters. Additionally or alternatively, each transmitter may be anysuitable MIMO transmitter; for example, transmitters may include MIMOsignal splitting or processing circuitry (which may be used to process asingle digital signal into multiple MIMO analog signals).

The first and second receivers 110 and 115 are preferablyimplementations having multiple inputs and outputs. In particular, eachreceiver preferably includes an ADC and frequency downconverter for eachreceive signal path; additionally or alternatively, receive signal pathsmay share ADCs and/or frequency downconverters. Additionally oralternatively, receivers may be any suitable MIMO receiver; for example,receivers may include MIMO signal splitting or processing circuitry(which may be used to process multiple MIMO analog signals into a singledigital signal).

In an embodiment of the relay 100 designed for MIMO operatingenvironments (i.e., multiple transmit and/or receive signals), the relay100 preferably includes analog self-interference cancellers 131 for eachpair of receive/transmit signals, as shown in FIG. 9. In MIMO operatingenvironments, self-interference may occur across communications streamsin addition to in them; for example, a TX1 signal may cause interferencein both of RX1 and RX2 signals. As a result, the relay 100 mayadditionally or alternatively include analog self-interferencecancellers 131 for self-interference cancellation across communicationsstreams, as shown in FIG. 11. Cross-stream cancellation may additionallyor alternatively be combined with cross-directional cancellation (whichis as shown in FIG. 6).

In an embodiment of the relay 100 designed for MIMO operatingenvironments (i.e., multiple transmit and/or receive signals), thedigital self-interference canceller 132 may perform digitalself-interference cancellation on each MIMO digital receive signal, butmay additionally or alternatively perform digital self-interferencecancellation on a combined digital receive signal (resulting from thecombination of MIMO digital receive signals). If the digitalself-interference canceller 132 performs self-interference cancellationfor multiple MIMO digital receive signals, cancellation may be performedfor each TX/RX pairing, similarly to those described in the section onthe analog self-interference canceller 131.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claims, modifications and changescan be made to the preferred embodiments of the invention withoutdeparting from the scope of this invention defined in the followingclaims.

We claim:
 1. A self-interference-cancelled full-duplex relay comprising:a first receiver, coupled to a first signal path of the relay, thatreceives a first analog receive signal at a first signal frequency viathe first signal path, and converts the first analog receive signal to afirst digital receive signal; wherein the first digital receive signalcontains a first message; a first transmitter, coupled to the firstsignal path of the relay, that converts a first digital transmit signalreceived via the first signal path to a first analog transmit signal,and transmits the first analog transmit signal at the first signalfrequency; wherein the first digital transmit signal also contains thefirst message; a second receiver, coupled to a second signal path of therelay, that receives a second analog receive signal a second signalfrequency via the second signal path, and converts the second analogreceive signal to a second digital receive signal; wherein the seconddigital receive signal contains a second message; a second transmitter,coupled to the second signal path of the relay, that converts a seconddigital transmit signal received via the second signal path to a secondanalog transmit signal, and transmits the second analog transmit signalat the second signal frequency; wherein the second digital transmitsignal also contains the second message; wherein the first and secondmessages are non-identical; wherein the first and second signalfrequencies are non-identical; and a first self-interference cancellerthat generates a first homo-channel self-interference cancellationsignal based on at least one of the first digital transmit signal andthe first analog transmit signal, and combines the first homo-channelself-interference cancellation signal with at least one of the firstdigital receive signal and the first analog receive signal, resulting ina reduction of self-interference in the first digital receive signal;wherein the first self-interference canceller further generates a secondhomo-channel self-interference cancellation signal based on at least oneof the second digital transmit signal and the second analog transmitsignal, and combines the second homo-channel self-interferencecancellation signal with at least one of the second digital receivesignal and the second analog receive signal resulting in a reduction ofself-interference in the second digital receive signal; wherein thefirst receiver may receive during transmission of the first transmitteror transmission of the second transmitter; wherein the second receivermay receive during transmission of the first transmitter or transmissionof the second transmitter; wherein the first and second receivers mayreceive simultaneously.
 2. The relay of claim 1, wherein the first andsecond receivers may receive simultaneously during transmission of bothof the first and second transmitters.
 3. The relay of claim 2, whereinthe first self-interference canceller generates the first homo-channelself-interference cancellation signal by combining filtered, scaled, anddelayed versions of at least one of the first analog transmit signal andthe first digital transmit signal; wherein the second self-interferencecanceller generates the second homo-channel self-interferencecancellation signal by combining filtered, scaled, and delayed versionsof at least one of the second analog transmit signal and the seconddigital transmit signal.
 4. The relay of claim 3, wherein the firstself-interference canceller generates the first homo-channelself-interference cancellation signal from the first analog transmitsignal in a radio frequency (RF) domain without performing frequencydownconversion; wherein the first self-interference canceller generatesthe second homo-channel self-interference cancellation signal from thesecond analog transmit signal in the RF domain without performingfrequency downconversion.
 5. The relay of claim 3, wherein the firstself-interference canceller generates the first homo-channelself-interference cancellation signal from the first digital transmitsignal in a digital domain; wherein the first self-interferencecanceller generates the second homo-channel self-interferencecancellation signal from the second digital transmit signal in thedigital domain.
 6. The relay of claim 2, wherein the firstself-interference canceller further generates a first hetero-channelself-interference cancellation signal based on at least one of the firstdigital transmit signal and the first analog transmit signal, andcombines the first hetero-channel self-interference cancellation signalwith at least one of the second digital receive signal and the secondanalog receive signal, resulting in a further reduction ofself-interference in the second digital receive signal.
 7. The relay ofclaim 6, wherein the first self-interference canceller further generatesa second hetero-channel self-interference cancellation signal based onat least one of the second digital transmit signal and the second analogtransmit signal, and combines the second hetero-channelself-interference cancellation signal with at least one of the firstdigital receive signal and the first analog receive signal, resulting ina further reduction of self-interference in the first digital receivesignal.
 8. The relay of claim 7, wherein the first and secondtransmitters are single-output transmitters; wherein the first andsecond receivers are single-input receivers.
 9. The relay of claim 7,wherein the first transmitter is a multiple-output transmitter; whereinthe second transmitter is a single-output transmitter.
 10. The relay ofclaim 9, wherein the first receiver is a multiple-input receiver;wherein the second receiver is a single-input receiver.
 11. The relay ofclaim 9, wherein the first receiver is a single-input receiver; whereinthe second receiver is a multiple-input receiver.
 12. The relay of claim7, wherein the first and second transmitters are multiple-outputtransmitters; wherein the first and second receivers are multiple-inputreceivers; wherein the first and second receivers contain multiple-inputmultiple-output (MIMO) processing circuitry; wherein the MIMO processingcircuitry of the first receiver receives a first set of multiple analogreceive signals and generates the first digital receive signal byprocessing the first set of multiple analog receive signals; wherein theMIMO processing circuitry of the second receiver receives a second setof multiple analog receive signals and generates the second digitalreceive signal by processing the second set of multiple analog receivesignals.
 13. The relay of claim 12, wherein the first self-interferencecanceller combines the first homo-channel self-interference cancellationsignal and the second hetero-channel self-interference cancellationsignal with the first digital receive signal; wherein the firstself-interference canceller combines the second homo-channelself-interference cancellation signal and the first hetero-channelself-interference cancellation signal with the second digital receivesignal.
 14. The relay of claim 13, wherein the first and secondtransmitters contain multiple-input multiple-output (MIMO) processingcircuitry; wherein the MIMO processing circuitry of the firsttransmitter processes the first digital transmit signal to generate andtransmit a first set of multiple analog transmit signals; wherein theMIMO processing circuitry of the second transmitter processes the seconddigital transmit signal to generate and transmit a second set ofmultiple analog transmit signals.
 15. The relay of claim 14, wherein thefirst self-interference canceller generates the first homo-channel andfirst hetero-channel self-interference cancellation signals from thefirst digital transmit signal and in a digital domain; wherein the firstself-interference canceller generates the second homo-channel and secondhetero-channel self-interference cancellation signals from the seconddigital transmit signal and in the digital domain.
 16. The relay ofclaim 15, further comprising a first relay base coupled to andpositioned between the first transmitter and the first receiver thatmanages retransmission of information contained in signals received bythe first receiver; further comprising a second relay base coupled toand positioned between the second transmitter and the second receiverthat manages retransmission of information contained in signals receivedby the second receiver.
 17. The relay of claim 16, wherein the firstrelay base delays signals to time retransmission with a transmissiontime window.
 18. A multiple-input multiple-output (MIMO)self-interference-cancelled full-duplex relay comprising: a firstreceiver, coupled to first and second signal paths of the relay, thatreceives a first analog receive signal at a first signal frequency viathe first signal path and a second analog receive signal at a secondsignal frequency via the second signal path, converts the first analogreceive signal to a first digital receive signal, converts the secondanalog receive signal to a second digital receive signal, and jointlyprocesses the first and second digital receive signals to generate afirst combined digital receive signal; wherein the first combineddigital receive signal contains a first message; a first transmitter,coupled to the first and second signal paths of the relay, that convertsa first digital transmit signal to first and second analog transmitsignals, transmits the first analog transmit signal at the first signalfrequency, and transmits the second analog transmit signal at the secondsignal frequency; wherein the first and second analog transmit signalsare combinable by a MIMO receiver; wherein the first digital transmitsignal also contains the first message; a second receiver, coupled tothird and fourth signal paths of the relay, that receives a third analogreceive signal at a third signal frequency via the third signal path anda fourth analog receive signal at a fourth signal frequency via thefourth signal path, converts the third analog receive signal to a thirddigital receive signal, converts the fourth analog receive signal to afourth digital receive signal, and jointly processes the third andfourth digital receive signals to generate a second combined digitalreceive signal; wherein the second combined digital receive signalcontains a second message; a second transmitter, coupled to the thirdand fourth signal paths of the relay, that converts a second digitaltransmit signal to third and fourth analog transmit signal, transmitsthe third analog transmit signal at the third signal frequency, andtransmits the fourth analog transmit signal at the fourth signalfrequency; wherein the third and fourth analog transmit signals arecombinable by a MIMO receiver; wherein the second digital transmitsignal also contains the second message; and a first self-interferencecanceller that generates a first homo-channel self-interferencecancellation signal based on at least one of the first digital transmitsignal, the first analog transmit signal, and the second analog transmitsignal, and combines the first homo-channel self-interferencecancellation signal with at least one of the first analog receivesignal, the second analog receive signal, the first digital receivesignal, the second digital receive signal, and the first combineddigital receive signal, resulting in a reduction of self-interference inthe first combined digital receive signal; wherein the firstself-interference canceller further generates a second homo-channelself-interference cancellation signal based on at least one of thesecond digital transmit signal, the third analog transmit signal, andthe fourth analog transmit signal, and combines the second homo-channelself-interference cancellation signal with at least one of the thirdanalog receive signal, the fourth analog receive signal, the thirddigital receive signal, the fourth digital receive signal, and thesecond combined digital receive signal, resulting in a reduction ofself-interference in the second combined digital receive signal; whereinthe first receiver may receive during transmission of the firsttransmitter or transmission of the second transmitter; wherein thesecond receiver may receive during transmission of the first transmitteror transmission of the second transmitter; wherein the first and secondreceivers may receive simultaneously.
 19. The MIMO relay of claim 18,wherein the first and second signal frequencies are identical; whereinthe third and fourth signal frequencies are identical.